Get Mac viewer working with SDL

tools/viewer/sk_app/mac/WindowContextFactory_mac.h

 
 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef WindowContextFactory_mac_DEFINED
 #define WindowContextFactory_mac_DEFINED
 
+#include "SDL.h"
+
 namespace sk_app {
 
 class WindowContext;
 struct DisplayParams;
 
 namespace window_context_factory {
 
 struct MacWindowInfo {
-#if 0 // TODO: use Mac-specific objects
-    Display*     fDisplay;
-    XWindow      fWindow;
-    XVisualInfo* fVisualInfo;
-#endif
+    SDL_Window*  fWindow;
 };
 
 inline WindowContext* NewVulkanForMac(const MacWindowInfo&, const DisplayParams&) {
     // No Vulkan support on Mac.
     return nullptr;
 }
 
 WindowContext* NewGLForMac(const MacWindowInfo&, const DisplayParams&);
 
 }  // namespace window_context_factory
 
 }  // namespace sk_app
 
 #endif